Introduction to web APIs

What's an API?

API stands for Application Programming Interface

... and here's a definition:

A set of functions and procedures allowing the creation of applications that access the features or data of an operating system, application, or other service.

Source: Oxford Languages via Google

Web APIs

Web APIs are used to exchange data via the internet, and typically have the following characteristics:

• resources are accessed via URLs with the structure:
  {base_url}{endpoint}

• support data transfer using standard HTTP methods:
  GET, POST, PUT, and DELETE

• data is transferred in the following formats:
  JSON(most common and what we'll focus on), XML or YAML

API URLs: Example

https://api.spotify.com/v1 is the base URL for the main Spotify API, onto which numerous endpoints can be added, such as:

/browse/categories
/artists/albums
/tracks/{id}

• the URL itself may be used to target more specific data
• You may see the term URI used instead (Uniform Resource Identifier)

GET and POST requests

Our focus will be on GET and POST methods (also known as requests), which are the methods typcially needed to access data from a web API.

GET: used to request data from the given resource
POST: used to send data to create or update a resource

GET requests

GET requests can contain a query string of key=value pairs in the URL to request more specific data

• for example: https://api.spotify.com/v1/browse/new-releases?country=SE&limit=10
• the endpoint is followed by a ? and key=value pairs, each separated by &
• these URLs can be cached, bookmarked, or held in the browser history; not secure

POST requests

POST requests can send data within the request body

• not cached, more secure; we'll use these for authorization to access data via the API
• although we're sending data, the term request is usually appropariate since we require a response